Google UK users (and perhaps other countries, too) were greeted to an amazing sight today: an interactive logo made out of colored balls. But why? Is Google demonstrating the power of HTML5? Celebrating the birth of kiddywinks' ball pits?

They've only done several interactive logos since their hugely successful playable Pac-Man game back in May. Saturday the 4th of September celebrated the 25th anniversary of the discovery of the buckyball, the carbon dome. The second "o" in Google showed a spinning ball which could be spun with the cursor—check it out in the first YouTube video below.

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Gizmodo reader Jason emailed me after the buckyball logo, to say that while some were complaining about Google's logo crashing their PCs and using up valuable CPU, the owner of GetBuckyballs.com (a website selling magnetic desktoys), saw terrific results. According to a tweet made on the 5th, he sold over 10,000 sets in just 24 hours. At $30 per unit, that's over $300,000 revenue, thanks to Google.

So what does today's logo mean? Normally Google's logos mark a birthday or anniversary, but so far everyone's scratching their heads over today's. There's no click-through for seeing relevant search results pertaining to the logo, and it's doubtful it's celebrating a Google birthday—they were founded on September 4, 1998, and the second birthday for Google Chrome was on the 2nd of September last week. I don't think it's related to Android either, with the announcement of the first Android phone, the G1, being on the 23rd of September, 2008.

Answers on a postcard (or below in the comments), please...

UPDATE: It appears to be available to US and UK users of Google, depending on browser versions.